West German Chancellor Helmut Schmidt appealed today for understanding from allies in the West and Communist neighbors in the East as West Germans grapple once again with the sensitive question of eventual reunification of the divided German nation.

Realistically, it is inconceivable that West Germany could be reunited with the Communist East, barring an extraordinary upheaval in superpower relationships and the present East-West military and economic alliances.

Nevertheless, there is a renewed debate on the subject here in the press and in political circles. It has been sparked mostly by vague remarks by some prominent left-of-center Bonn politicians and by outside commentaries suggesting that West Germany eventually might be tempted to become neutral in return for some kind of a deal with Moscow for reunification with the third of prewar Germany now within the Soviet-led War-saw Pact.

One result of the public debate is that Bonn has received some "signals of irritation" from Poland, which has good relations with West Germany today but which has historical reason to fear a reunited Germany; from East Germany, with which Bonn began to normalize relations in 1972, and even from some of West Germany's North Atlantic Alliance partners, including the United States, government officials here say.

The complication for West Germany, however, is that the goal of eventual reunification of the German people-however unrealistic-is part of the West German constitution and is Alliance policy. Thus, the topic must be addressed periodically and one traditional platform is the chancellor's annual state-of-the nation address to the Bonn parliament. Schmidt delivered the speech today and dwelt heavily on the delicate reunification issue.

The chancellor reaffirmed this country's alliegiance to the West while seeking to make clear that he would not turn his back on the long-term constitutional goal of unification. He stresssed the advantages to all Europeans, East and West, of detente while indirectly reassuring countries such as Poland that Bonn was not seeking to re-create an empire.

"We have long ago accepted the existence of a second German state," Schmidt said in the nationally televised speech. "But we would deny our responsibility if the thought of one nation were given up. The Poles did not do that either, despite a long, long separation" of their nation.

"What will become of the German nation is not only a question of concern to the German people, but also for our neighbors in Europe and our partners in the alliances to which the two German states belong," Schmidt said.

"We have to recognize that we Germans don't get viewed by other nations with the same composure as others are looked at because the idea that someday a state of 75 million Germans could develop in Central Europe creates fear among many of our neighbors and partners.

"We have to accept that we Germans and the developments between and within both states are watched conscientiously, carefully and, at the moment, very critically by many foreigners.

"We must not forget that others see the division of Germany today as part of the balance of power that ensures the peace in Europe. Our neighbors and partners know that very well so we can only hope for their understanding if we approach our national question in a circumspect, careful and realistic manner-meaning with careful consideration of the interests of all our neighbors."

The chancellor warned that "with our geopolitical condition and recent history, Germany cannot afford political schizophrenia that on one hand makes a realistic peace policy and at the same time carries on an illusory reunification debate."

"Our European peace policy is founded on the steady anchoring of the Federal Republic of Germany in the Western alliances, and especially on close cooperation with France and friendly partnership with the United States and Great Britain," he said.

Aside from those relationships, Schmidt feels strongly that West Germany's ostpolitik, or "Eastern policy" of improving relations with former enemies in what is now Communist East Europe has also paid off.

The fear that these relations could quickly worsen if U.S. Soviet relations sour and uncertainty over the future U.S. role in the world that have stirred many West Germans, including Schmidt, to consider what other long-term possibilities there are for the German nation.

The chancellor's failure in recent months to dissociate himself clearly and quickly from some of the more controviersial attitudes of his Social Democratic Party parliamentary floor leader, Herbert Wehner, added to the priority that Bonn was thinking new thoughts. Wehner, 72, is a powerful figure on the left wing of Schmidt's party. In addition, many Western diplomants here privatley have expressed the view that the chancellor is overly solicitous of the Soviets these days.

Schmidt does not like to use the word reunification. Rather, in an attempt to put a fresh face on the concept, he prefers to speak of Germans who, in the very long run, are able to "once again live under one roof," a vague reference to a distant world in which East and West Germany could draw together economically and culturally but unofficially.

"But anyone who has confronted the problems of German division knows that reunification, that mutual roof for all Germans, is only possible if East and West indeed will be able to free themselves of the highly charged military polarization," Schmidt said today.

"There is a long, long way ahead of us to reach that point and for that reason we do not know today if, when and in what way German unity can be achieved." One thing is certain, he said: It is achievable only after a "long" peace.